Electromagnetic device having a permanent magnet armature



Nov. 16, 1965 H. E. BENSON 3,218,523

ELECTROMAGNETIC DEVICE HAVING A PERMANENT MAGNET ARMATURE Filed July 29,1963 I O I I I INVENTOR H20 for E, fielzs'on W ab Eh I BY ATTORNEYSUnited States Patent 3,218,523 ELECTROMAGNETIC DEVICE HAVING A PERMANENTMAGNET ARMATURE Hector Eugene Benson, Cheveley, Newmarket, England FiledJuly 29, 1963, Ser. No. 298,250 2 Claims. (Cl. 317172) This inventionrelates to direct-current tractive electromagnet devices, of whichsolenoids, relays and the like are common forms.

It is normal practice to make iron parts of electromagnets entirely offerrous material which is magnetized by the excitation of a coil orcoils and which ceases to be magnetized when the current is switchedoff. The armature or plunger of such an electromagnet device, therefore,requires the continuous passage of current through the coil in order tohold it in the closed position, unless otherwise achieved by amechanical latch.

It is an object of the present invention to enable the armature orplunger of a DC. electromagnet device, once closed by brief coilexcitation, to remain closed with current switched off and without theaid of a mechanical device, and to be released by a further coil pulseof reversed polarity.

According to the invention, the moving armature or plunger of theelectromagnet device consists wholly or partly of a permanent magnet,which in the open position lies sufficiently far away from a fixed polepiece in the electromagnet coil, not to move spontaneously towards thefixed pole piece under influence of its own permanent magnetism, orwhich in the open position magnetically attaches itself to a fixed pieceof ferrous material in order to restrain it from spontaneous closing.

Energizing of the electromagnet coil with direct current of the correctpolarity causes the permanent magnet armature to close by interaction ofthe permanent magnet and electromagnet fields, and in closing to exertexternal mechanical force in the manner known for tractiveelectromagnets of which solenoids and relays are common forms.

Once closed, the permanent magnet armature will contact the fixed polepiece and because of its magnetism, will be attracted thereto and remainclosed, sustaining whatever mechanical load is within its power, withoutfurther passage of current in the coil.

The armature or plunger is restored to the open position by energizingthe coil with current of reverse polarity to the closing current, sothat interaction of permanent magnet and electromagnet fields results inmutual repulsion of the fixed and moving parts.

One manner of using this principle is to apply reverse current of thesame strength as the closing current, to produce definite repulsion ofthe armature or plunger. An alternative manner is to apply a reversecurrent weaker than the closing current, sufiicient to cancel attractionof the fixed and moving parts but without repelling force.

The present invention will now be described in greater detail by way ofexample with reference to the accompanying diagrams, wherein:

FIG. 1 is a diagrammatic view of a form of the invention wherein a coilencircles a fixed pole piece to which a moving armature is pivotallyattached;

FIG. 2 is a diagrammatic view of a form of solenoid electromagnetwherein the moving plunger enters the coil; and

FIG. 3 illustrates a modified form of switching arrangement.

In each of the illustrated embodiments a yoke 1 or 1a defines a fixedpole 2 or 2a and is energized by a coil 3 or 3a. The armature 4 orplunger 4a is composed either wholly or partly of a permanent magnet,the effect in either case being to present magnetic poles of unlikepolarity at opposite ends of the moving part. Characters 5 and 5aidentify stops of ferrous material to which the armature or plunger mayreleasably attach itself by magnetic attraction when in the openposition. The stops 5 or 5a are mounted on any suitable fixed support(-not shown).

It will be evident that in each form, the coil may be energized withdirect current applied in such direction as to, selectively, attract orto repel the permanent magnet armature or plunger.

The ganged switching arrangement shown at 6 and 6a illustrates one wayin which current may be sent through coils 3 or 3a in either desireddirection and the modified switching arrangement 6b of FIG. 3illustrates a resistor 7 in one side of the circuit so that more currentwill flow in one direction than in the other.

The above described examples have been found to have the followingadvantages:

Only a momentary coil pulse is required to close or to open theelectromagnet, which by permanent magnet attraction will sustain itsload without current, without coil heating, and without the tendency todeterioration of insulating materials caused by coil heating.

The repelling effect of the reverse-polarity opening current can drivethe armature or plunger out to the open position, and take the place ofthe spring return frequently necessary with conventional electromagnets.

The same repelling effect can be used to achieve a double-actingsolenoid which without the benefit of this invention, necessitates theuse of two separate coils each with its own iron circuit.

The same repelling effect can give much faster opening than is possiblein a conventional D.C. electromagnet in which it is necessary to waitfor the decay of flux in the magnetic circuit before the armature orplunger can drop out.

I claim:

1. An electromagnetic device comprising: a coil; means for selectivelydirecting electric current to flow in either direction through saidcoil; a ferromagnetic pole piece in said coil and having a pole facetherein; a member mounted adjacent said pole piece for movement of atleast one portion of said member toward and from said pole face; saidmember being a permanent magnet and said one portion being one magneticpole thereof, said pole piece having another pole face adjacent anotherportion of said member which comprises the other magnetic pole thereof;a ferromagnetic stop member, separate from said pole piece, fixed inspaced relation to said pole face and said coil; said member beingengageable with said pole piece or with said stop member, selectively,to be magnetically held thereby in either of two positions.

2. A device as defined in claim 1 wherein said pole piece comprises agenerally U-shaped member with said coil surrounding one leg thereof;said member being piv otally mounted on the other leg of said polepiece, in the region of its said other magnetic pole.

References Cited by the Examiner UNITED STATES PATENTS 2,740,956 4/1956Hatton 317-172 X 3,119,940 1/1964 Pettit et al 31717l X 3,126,501 3/1964Flora 317171 X BERNARD A. GILHEANY, Primary Examiner.

JOHN F. BURNS, Examiner.

1. AN ELECTRONAGMETIC DEVICE COMPRISING: A COIL; MEANS FOR SELECTIVELYDIRECTING ELECTRIC CURRENT TO FLOW IN EITHER DIRECTION THROUGH SAIDCOIL; A FERROMAGNETIC POLE PIECE IN SAID COIL AND HAVING A POLE FACETHEREIN; A MEMBER MOUNTED ADJACENT SAID POLE PIECE FOR MOVEMENT OF ATLEAST ONE PORTION OF SAID MEMBER TOWARD AND FROM SAID POLE FACE; SAIDMEMBER BEING A PERMANENT MAGNET AND SAID ONE PORTION BEING ONE MAGNETICPOLE THEREOF, SAID POLE PIECE HAVING ANOTHER POLE FACE ADJACENT ANOTHERPORTION OF SAID MEMBER WHICH COMPRISES THE OTHER MAGNETIC POLE THEREOF;A FERROMAGNETIC STOP MEMBER, SEPARATE FROM SAID POLE PIECE, FIXED INSPACED RELATION TO SAID POLE FACE AND SAID COIL; SAID MEMBER BEINGENGAGEABLE WITH SAID POLE PIECE OR WITH SAID STOP MEMBER, SELECTIVELY,TO BE MAGNETICALLY HELD THEREBY IN EITHER OF TWO POSITIONS.